I propose to measure variation in oxidative stress response across individuals and populations, and to identify the genetic loci that are associated with such variation. Oxidative stress has been strongly implicated in the etiology of age-related disease and as a determinant of longevity. Pathways that mediate oxidative stress response have been extensively studied, but we still know relatively little about individual variation in th function of these pathways. Understanding the factors that govern variation in oxidative stress response across individuals may improve our understanding of age-related disease and physiological decline. Here, I propose a series of experiments and statistical analyses to study the genetic basis of variation in oxidative stress response. Specifically, in Aim 1, I will purify CD4+ T cells from 70 Caucasians and 70 African Americans. I will expose these cells to oxidative stress for 72 hours by culturing them in elevated (20%) oxygen levels, while maintaining control cells from the same individuals in physiological (5%) oxygen levels. At specified time points during this period, I will measure the ratio of oxidized glutathione to reduced glutathione (an indicator of oxidative stress); the ratio of oxidized guanine to unmodified guanine (an indicator of oxidative stress-induced DNA damage); and genome-wide mRNA abundance, in both treated and control cells. In Aim 2, I will collect genotypes from all samples used in aim 1 and map quantitative trait loci (QTLs), including expression QTLs, that explain variation in oxidative stress response. Reporter gene assays will then be used in Aim 3 to validate approximately 30 of the putative eQTLs.